Evening Exercise Does Not Differentially Influence Sleep Outcomes Compared to Morning Exercise

PURPOSE: To determine the influence of morning or evening exercise on accelerometer-determined sleep outcomes. METHODS: Thirty-seven healthy and young individuals were randomly assigned to a morning (n=18) or evening exercise group (n=19). Within each group there was an exercise and non-exercise condition, counter-balanced and determined randomly. Participants in the morning exercise group reported to the laboratory between 7-10am, completed a 45-minute bout of moderate-intensity exercise, and then wore an accelerometer (at hip and wrist) for 24 hours. Their non-exercise day was identical except there was no morning exercise. Participants in the evening group reported to the laboratory between 7-10pm, completed a 45-minute bout of moderate-intensity exercise and then wore an accelerometer (hip and wrist) for 24 hours. Their non-exercise day was identical except there was no evening exercise. Sleep data were analyzed using ActiLife Data Analysis Software. Bed times and wake times were determined using the auto function in the ActiLife software. The age-appropriate Sadeh equation was utilized to determine total sleep time, sleep efficiency, number of awakenings, and sleep latency. The data below are from the hip-placed accelerometer. RESULTS: Total sleep time (TST) in the morning exercise group was 7.38±1.54 hrs during the exercise condition and 7.71±1.63 hrs during the non-exercise condition (p=0.44). TST in the evening exercise group was 7.65±1.38 hrs during the exercise condition and 7.25±2.32 hrs during the non-exercise condition (p=0.22). The group*condition interaction was not significant for TST (F=0.78; p=0.38) or other sleep outcomes (p>0.17).There was not a main effect of exercise for any sleep outcome (p>0.49). Results were not different using the wrist accelerometer data. CONCLUSION: When examined experimentally, a 45-minute bout of exercise either in the morning or evening did not influence accelerometer-determined sleep outcomes positively or negatively.